Why do some people think this is accurate?
The cost to mine 1 BTC varies a ton depending where you are at, so this would mean if you are from China the cost will be cheaper than in Canada for instance, but this is not all. There are many other variables.
So you would need to create a global average I guess, but even then, how is this accurate?
Electricity cost is not equal in all countries, and because of that mining bitcoin is not equally profitable. Those who are confused by this, doesn't know enough about mining. And I guess it would be impossible to make global average price for mining, I don't see point for that.
How could 1 unit of Bitcoin be only worth it's cost to mine one (which by the way I think it's around the current price) when it's marketcap is so tiny?
I am not sure if that is correct, those odds sounds a bit crazy if you ask me. No one would mine BTC if they would need 1 BTC to mine one back. Also, bitcoins cap is large enough if you ask me.
It's insane to assume that you have to wait until 2140 to reach "the moon". Bitcoin's features are the same irrespective of how many halvings away we are from that. The cost of mining one doesn't reflect it's true value. The hashrate is strong enough to be as safe as it gets to use a store of value. If anything, it shows me that it's insanely undervalued.
Maybe BTC will never reach "the moon" , everything is possible after all. Also you are correct about true value of BTC, but I'm not sure if its undervalued. I know for sure that it will stay as volatile, as long as people are looking on BTC as an investment and not for what it is.